Tech Issues in GIS
Tech Issues in GIS GISC 425
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This 32 page Class Notes was uploaded by Jamaal Lakin on Monday October 12, 2015. The Class Notes belongs to GISC 425 at Ferris State University taught by Robert Burtch in Fall. Since its upload, it has received 35 views. For similar materials see /class/221618/gisc-425-ferris-state-university in Exercise Biology at Ferris State University.
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Date Created: 10/12/15
GISC 425 Technical Issues in GIS and Cartography Metadata Adapted from the notes of Dr Yamn Metadata Surveying Engineering Ferris State University iimmm Genelamn i Process METADATA I Data about data I Federal Geogra hic Usually an XML Data Comm39ttee document FGDC adopted I Describes data content standard on content June 8 1994 quality condition I Executive Order other characteristics 12906 requires all federal agencies to use standard effective January 1995 GISC 425 Technical Issues in GIS and Cartography What is Metadata Ti rle sufplemen ral in or ma rion absfr39ac r mamm 1 p AiringJimmy What is Metadata Nutriti Wm WM Sewmwmmem len r if I of T r39 i b u T mmyvmmhmumaznnn MW nas 200 cxczvmm 1 p MRIQnRUMM m a cgvmmww Pym4 Metadata GISC 425 Technical Issues in GIS and Cartography Metadata Examples of Metadata Identification Title Area covered Themes Currentness Restrictions Data Quality Accuracy Completeness Logical Consistency Lineage Spatial Data Organization Indirect Vector Raster Type of element Number Spatial Reference Projection Grid system Datum Coordinate system Entity and Attribute Information Features Attributes Attribute values Distribution Distributor Formats Media Online Price Metadata Reference Metadata currentness Responsible party From Metadata Workbook Objectives I Supports common uses of metadata Internal investment clearinghouse ransfer I Developed from the perspective of what do I need to know about a data setquot Availability fitness access transfer I Provides a common set of terminology and definitions and information about values to be provided f I Identifies mandatory mandatory td applicable and optional data elements From Metadata Workbook GISC 425 Technical Issues in GIS and Cartography Metadata VALUE OF METADAT 1 I Data can be used almost 39 39 instantaneously through a network for different analysis I Data can be transformed and then retransmitted for further use I Helps user nd and use geospatial data I Lack of knowledge of available data leads to duplication of work WHAT IS METADATA I Desc p ve information to digital b I Common set of de nMonsand tennsusedin documenm on I Analogy map legend Publisher Publication Date scale amp accuracy Type of map Spatial references etc GISC 425 Technical Issues in GIS and Cartography DATA PRODUCER BENEFITS I Data that is undocumented may lose its value I Assures future use of data If no metadata present future users may have little understanding of both contents and uses therefore may not trust the results METADATA PROVIDES USER WITH KNOWLEDGE OF DATA I What data are available I Does data meet specific needs I Where can data be found I How can data be accessed Metadata GISC 425 Technical Issues in GIS and Cartography MAJOR USES OF 1ETADATA I Helps organize and maintain organization s internal investment in data I Provides information on organization s data holdings I Provides information to process and interpret data CHARACTERISTICS ON ROLE OF METADATA I Availability I Access What data sets exist Data needed to for a geographic acquire an identi ed location set of data I Fitness for Use I Transfer VWI the data set Data needed to meet a speci ed process and use set need of data Metadata GISC 425 Technical Issues in GIS and Cartography From Metadata Workb ook DATA ELEMENTS DEFINED IN STANDARD Identification Data Quality Information Information Assessment of quality of Rules about data d3 3 59 set positional and attribute me area of accuracy completeness Y sources of informa I currency mes for methods used to produce acquiring and data using data Metadata GISC 425 Technical Issues in GIS and Cartography Metadata DATA ELEMENTS DEFINED IN STANDARD I Spatial Data I Spatial Reference Organization Information Information Description of Mechanism used to reference frame represent information map projection in data set parameters or grid rastervector street coordinate SYStem addresses or county horizontalvertical codes etc datum coordinate system resolution DATA ELEMENTS DEFINED IN STANDARD I Entity and Attribute I Distribution Information Information Entity types and their How data can be attributes and obtained domains from contact person attribute values may formats fees be assigned names amp definitions of features attributes amp attribute values GISC 425 Technical Issues in GIS and Cartography DATA ELENTENTS DEFINED IN STANDARD l MultiUse Sections I Extensibility Templates allOWlng Produceruser can one to re39use pro le and extend metadata elements standard beyond the in various sections base standard Same contact information may be Meets organizational used in Identi cation 0 dlSClPllne Information and metadata Distribution requirements Information sections Metadata Data quality DataQuaitynformation AttributeAccuracy LogicalConsistencyReport CompletenessReport PositionaAccuracy Lineage CIoudCover We will look at each of the elements in this equation define it and analyze ways to asses it Metadata GISC 425 Technical Issues in GIS and Cartography Section 2 csuwmmanz mm Data mam mu 5m am W Max mormanon 2 Data Quality Information mmm mm mm mm Ass 5mm mquot be new mu ms Humanm mm kcumm mm mm mm Wm mm WW mm mm H mmm mm mm mm Assam Amarammquot an be mm mm em I Mmemmquot mquot be mm mm mm Identify the errors in the map and Happy Valey Scale 110039 From Dr Yamn Fems ELmnwnuuwn um Metadata GISC 425 Technical Issues in GIS and Cartography Mctadata Example solutions Frnm Dr Yarnn F21 G Positional Accuracy I An assessment of the accuracy of the osition of s atial obects Precision defined as the number of decimal places or significant digits in a measurement Accuracy defined as the closeness of the location information usually coordinates to the true position GISC 425 Technical Issues in GIS and Cartography Positional accuracy 39 Methods for assessment Deductive Estimate Analyzing the process using error propagation 2 2 2 2 2 2 2 cab Ogc0phoatooroop0ob I odb estimated overall accuracyogc ground control I Internal Evidence Tests which are based on repeated measurement 2 X 7 RMSE Z S n Frnm Dr Yarnn F21 I Unclosed polygons overshoots and undershoots are indications I I lg Metad ata Data quality Estimation of positional accuracy Relative Compare 10 distances between distinct points on the map and on the ground Absolute Compare 10 coordinates of distinct points on the map and on the ground map map map gmmd ground ground Frnm Dr Yarnn F21 Calculate the RMS of the results Mctadata GISC 425 Technical Issues in GIS and Cartography Metadata Data quality Estimation of completeness and attribute accuracy Subdivide the area into small sections examine the map in the field and check for omittedwrongly classified entities Frnm Dr Yarnn F21 Area Sheet Missing water Missing water Missing re Other Number manholes Valves meter hydrants 1232 l4 l6 l1 Fencemissing Thorough analysis of the spatial database to estimate logical consistency Positional accuracy Methods for assessment l Checking using independent source of higher accuracy Example for a standard I quotASPRS accuracy standard for large scale maps Horizontal accuracy Map scale 1500 m Root Mean Square Error 0125 m vertical accuracy onethird ofthe indicated contour interval for well defined points only Spot heights shall be shown on the map within a limiting RMS error of onesixth of the contour interval Frnm Dr Yarnn F21 Metadata GISC 425 Technical Issues in GIS and Cartography Metadata Frnm Dr Yarnn F21 Attribute Accuracy I Attribute data describe geographic entitie I An assessment of the accuracy of the identification of entities and assignment of attribute values in the data set I Assessment of quality Deductive Estimate an estimate based on experience Tests Based on independent samples for example field checking for incorrect attributes eg water manhole identified as sewage manhole Frnm Dr Yarnn F21 Logical Consistency I Describes the fidelity of relationships encoded in the da correct progression of contour values roads connecting with other roads Electricity network connected 1r all land unIts I Assessment 5 Tests of Valid Values General Tests for Graphic Data Do lines intersect Are there any overshoots or undershoots GISC 425 Technical Issues in GIS and Cartography Metadata From Dr Yaroll Felus Completeness information about selection criteria Assessment of completeness Duplicate surveys Superimpose the vector map on the screen Standards 11250 scale map all permanent objects or building which covers an area of 8 m2 or more will be shown as a matter of routine Smaller buildings or objects may be included where they are in a detached position OSGB From Dr Yaroll Felus Lineage A description of the source material from which the data were derived and the methods of derivation including all transformations involved in producing the final digital files I Who did the map When Why How and so forth GISC 425 Technical Issues in GIS and Cartography Map Generalization Surveying Engineering Department Ferris State University m Elements of Cartographic Generalization Simplification 0 Determine important characteristics of data eliminate wanted detail retain and possibly exaggerate important characteristics Classification 0 OrderingScaling and grouping of data Sym bolization 0 Graphic coding of scaled andor grouped essential characteristics comparative signi cances and relative positions Induction 39 0 Application of logical process of inference Map Generalization GISC 425 Technical Issues in GIS and Cartography Map Generalization Controls of Cartographic Generalization 0 Objective 0 Purpose of map 0 Scale 0 Ratio of map to earth 0 Graphic Limit 0 Capability of system used to make map and perceptual capabilities ofviewers 0 Quality of Data 0 Reliability and precision of various kinds of data being mapped Why Generalize Maps GISC 425 Technical Issues in GIS and Cartography Effects of Change in Scale small SLGt rr uuyunu quotmumquot mummy SmallerScale Maps ore area 0 LargerScale Maps e55 area L Less detail More detail More generalization Less generalization More classification Less classi cation Simplification o Features like roads buildings small streams only delineated without being significantly enlarged on largescale plane ie 1250 o Two primary objectives 0 To t information to the capability ofthe map to portray it as a chose 0 Maintain essential geographic characteristic of mapped phenomenon Symbols take up room on map as map scale get smaller less and less data can be shown 0 Initially select only necessary classe fdat a 0 Eliminating some of data by reducing linear complexities Map Generalization GISC 425 Technical Issues in GIS and Cartography Simplification 0 Relative map space available a function of scale 0 Reduction takes place as square of ratio of differences in linear scale 0 Scale reduction compresses space allowing limited portrayal o What to discard and what to retain depends on 0 Relative importance of item 0 Relation of class of data to objectives of map 0 Graphic consequences of retaining an item CCRS l CCT Simplification l 69 ill M39 l 5 139 tr 6 III A I A y t39 a I 4 7s ll 0 r w l l f I Wi was ill a a 7 t vb h of Q rvs l i n G h Map Generalization GISC 425 Technical Issues in GIS and Cartography T pfer s Radical Law 0 Basic form 0 Basic principle ratio of scale of compiled and source map 0 Problem of simplification nature of data Islandslakes shown without exaggeration Symbols take up more space nc CeCfns Ji i T pfer s Radical Law o Constant of symbolic o Constant of symbolic exaggeration Ce C 1 normal symbolization wo exaggeration Ce2 3330 features of areal extent shown in outline shown wo exaggerai n likelakesislands 39 Ce3 ScSs C 1 symbols compiled wo essential change of2 w5wcScSs for linear symbols where widths of lines on source ws and newly compiled map we are important in generalization of3 asacScSs2 for Map Generalization symbolization involving great exaggeration on required map like settlement symbols with associated names area symbols where areas of symbols on source as and newly compiled ma ac are important items in generalization GISC 425 Technical Issues in GIS and Cartography Simplification Determining which data elements to retain and which to eliminate difficult task Choice can be deduced from purpose of map and visual distribution knowledge of data being mapped Distinctive characteristics need to be retained When objective of map demands it simplification must become diagrammatic Classification 0 Instead of eliminating detail mm m VEV39UMMUNmEswLF classification attempts to typify 0 Group phenomena to bring simplicity to complex differences or unmanageable magnitudes of data 0 Common processes 0 Allocation of similar qualitative na in 0 ca egories or quantitative data into de ned groups 0 Selection of location and modi cation of data at that location to simulate typical data elements a the area Map Generalization GISC 425 Technical Issues in GIS and Cartography Classification Dot Densin 1900 Dot Density 2000 m We Symbolization o Assigning marks to summarize results from classification 0 Essential characteristics 0 Comparative significances 0 Relative positions 0 All marks on maps are symbols Map Generalization GISC 425 rTechnicaI Issues in GIS and Cartography SelectionElimination 0 Select elements to appear on map 0 Two methods Select entire feature like Selection within feature categories ie select group of he ses but not othe s Amalgamation o Grouping merging or coalescing features 0 Example if several individual houses s source map buti de merged to form blocks on rived map individual houses REL summer Map Generalization GISC 425 7 Technical Issues in GIS and Cartography Collapse 0 Double line features like hydrographic network or roads need to be collapsed for single line representation when signi cant scale change 0 Area features like lakes can be collapsed to line features in river network eccusrccr Exaggeration 0 Increase spatial extent for Emphasis Legibility 0 Example enlarging size ofisland which would otherwise be small enough to remove in EECRsccv Map Generalization GISC 425 Technical Issues in GIS and Cartography Typification Reduce density of objects while maintaining representative distribution 0 Example islands reduced in density to eliminate crowding while maintaining original character of cluster 0 In next figure island cluster reduced in density and shifted in effort to maintain character of the distribution Linear Simplification Algorithms Independent point routines Local processing routines o Unconstrained extended local processing routines ReumannWtkam algorithm 0 Constrained extended local processing routines Opheim algorithm Land algorithm Johannsen algorithm Global routines o DouglasPeuker algorithm Map Generalization GISC 425 Technical Issues in GIS and Cartography Map Generalization Independent Point Routines Simple Do not account for topological relationship of points Two basic methods 0 nm point routine every 3rd or 5th or whatever point retained o Randomly select Inm points Local Processing Routines Euclidean distance between points Angular change between points 0 Perpendicular distance and angular change tsunami mums comm mum mmquot GISC 425 Technical Issues in GIS and Cartography Jenk s Simplification Algorithm Based on 3 userdefined Min 1 parameters o Max 1 l i A I I V l l l 39 l VI 1 l eliminate p2 l 39 VI 1 Am i 93 gig L l B 2 pvhan MINI USER 1 F greats DEFINAELE r D mime p2 1 5 Am PARAMETERS RETAIN p2 C greater than MINE 2quot D p geae than MINI H i J x 39 mama a w t t M R 39 x 9 z Unconstrained Extended Local Processing Routines 0 Search beyond immediate neighboring coordinate pairs 0 Evaluate sections of line Extent of search depends on Complexity of line Density of coordinate set Beginning point for the sectional search Map Generalization GISC 425 Technical Issues in GIS and Cartography ReumannWitkam Simplification Algorithm Uses 2 parallel lines A to define search region 73 0 Calculate initial slope t of search region 0 Line processed sequentially until one of edges of search corridor intersects line 1r Opheim Simpli cation Algorithm 0 Like ReumannVWtkam 0 Algorithm constrained by min quotf and max distance check like a Jenks g L 0 after initial search region set up any points within DMIN are eliminated 0 Soon as line escapes from 9 35 a search region on any side c J including DMAX at end new 5 search corridor started and last point in region saved a A J I fquot Map Generalization 13 GISC 425 Technical Issues in GIS and Cartography DouglasPeucker Algorithm 0 Select tolerance band or corridor 0 From corridor compute perpendicular distances to all intermediate points to determine one farthest away point stored 0 Next new corridor calculated between first point and stored point 0 Compute perpendicular distances to intermediate points 0 Process continued throughout line DouglasPeucker Algorithm Map Generalization GISC 425 Technical Issues in GIS and Cartography Map Generalization Llno Slmpllflcatlon Douglas Peuckor algorlthm 1 Defines a straight line segment between the first point and the last point on a polygon 2 Perpendiculars between the line segment and each of the original points are measured The distance from Ax By C 0 to P1 Xin is d Ax1By1 c xA 32 tolerance Value GISC 425 Technical Issues in GIS and Cartography Line Simpli cation Douglas Peucker algorithm 3 If any of the intermediate points fall outside the tolerance band the line is split into two parts at the furthest point point 9 and the process is continued on the two resulting parts If the length of all perpendiculars is less than the present tolerance value the line segment is deemed adequate to represent the line all points with perpendicular length smaller then tolerance are deleted and the algorithm is A terminated 3 3 Example 4 e E Given the following 2 Six points with 1 3 Tolerance 10 5 Doulas Peucker alorithm example Example Compute the DouglasPeucker simpli ed line Point X Y Distance to Distance to Distance to coordinate oordinate line 16 line 136 line 1356 10 0 38 42 1 Z Z 71 1 96 Slide developed by v Felus 3 6 1 5 Map Generalization GISC 425 Technical Issues in GIS and Cartography Map Generalization Doulas Peucker alorithm example ExampleCompute the DouglasPeucker simplified line Equation ofline 16 is 0186X 1Y 8139 O The distance to point 2 l5 0 d V01862 12 Dashed line original Solid line Simpli ed 569 Sllde developed by v Felus Doulas Peucker alorithm example the line Sllde developed by v Felus
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